This invention relates to a suspension device of a vehicle such as an automobile and, particularly, to a suspension device of the kind comprising a hydraulic damper and an air spring associated therewith.
A suspension device of the aforesaid kind is publicly known, as shown in U.S. Pat. Nos. 3,039,760, 3,363,893, and 3,967,363, wherein a variable volume air chamber constituting the air spring is formed between the upper end portion of a tubular main body of the hydraulic damper and the upper end of a piston rod of the hydraulic damper which projects upward from the main body. By adjusting the pressure in the air chamber, it is possible to adjust the level of the vehicle in response to such as the loading of the vehicle. The spring rate of the air spring is determined by the volume of the air chamber and the pressure of the air, and thus, there is a problem that it is not possible to adjust the spring rate of the air spring as desired. Japanese Utility Model Disclosures Nos. (Kokai) 58-161710 and 59-53107 show a suspension device wherein the air chamber in the air spring is partitioned into a variable volume main air chamber and a constant volume sub chamber, and a valve is provided between the two chambers for selectively permitting or interrupting communication therebetween. In adjusting the level of the vehicle the two chamber are communicated together and the pressure in the air chambers is adjusted, and thereafter by closing the valve to separate the two chambers the suspension takes a hard condition. However, it is further desired to adjust the spring rate of the air spring at multiple steps, and to generate a damping force by the air spring unit.